Baffle necessary for every rafter?

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  #1  
Old 09-23-06, 07:01 AM
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Baffle necessary for every rafter?

On one side of my 27 yr old home (new to me) half of the roof has insulation in the rafters from the soffits up to the attic floor (about 10-15 ft), the other half of that side is a cathedral ceiling. On the cathedral ceiling half of the roof there are two soffit vents, but there are no soffit vents on the other half of that side where there's insulation in the rafters. We had our first frost the other night and the half of the roof with no vents and insulation in the rafters had frost on the shingles. The other side of the roof has soffit vents and no issues.

I need to add insulation to the attic floor, but before I do that I need to take care of the insulation in the rafter and soffit vent issue. How many soffit vents are needed and will I need to add baffles in every rafter that has insulation (10-15 ft) from soffit to the attic floor or just the rafters that have the new soffit vents?
 
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Old 09-25-06, 04:10 AM
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Do you think frost on the shingles is a bad thing? Frost is a natural phenomenon that indicates a couple things about the temperature of your roof compared with the heat loss from your home. Frost on the shingles on the one side of your house indicates that no heat is being lost from the house which would melt the frost, and the attic space must be sufficiently cold to allow frost to form. No frost on the cathedral side indicates that you are losing so much heat from the home that it is melting the frost, and that there is not enough cold air being introduced above the insulation (or distance separating the roof and insulation) to counter this effect.

It's pretty tough to say what you need for ventilation from just your description. That's something that a person usually has to look at and calculate depending on what type of exhaust is used at the top of the roof. But in answer to your question, baffles are not usually used in every rafter bay, unless you are using some type of continuous soffit vent.
 
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Old 10-02-06, 06:20 PM
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To piggy-back here ...

What if you don't have soffit vents? We have about a one foot overhang, and no apparent soffit vents in the aluminum siding. We do have a ridge vent. We want to finish the attic, with a three foot knee wall. We plan to insulate the roof [sloping walls and about a two foot wide ceiling] and the knee wall. Do we need baffles between all the rafters?

Is there a less expensive alternative than the pre-formed pink baffles?
 
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Old 10-03-06, 01:30 PM
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If you plan to insulate between the rafters in your ceiling, you must leave space above your insulation. Packing the rafters full of insulation would not be the best option. So regardless of whether or not there is currently soffit venting, I would suggest that you use the baffles in every rafter bay. An alternative might be installing some pieces of rigid foam 1x2 along the sides of the rafters, then glue a piece of rigid foam between every rafter to kind of make-your-own baffle... but whether or not that would cost less would be debatable.

At any rate, allowing for venting now in every rafter bay would allow for anyone in the future to add soffit venting or a continuous fascia vent, or even the cor-a-vent roof edge venting, and achieve some measure of ventilation.
 
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Old 10-03-06, 02:07 PM
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Thanks, Sleeper, baffles in every rafter space from the knee wall to the ceiling [which is far as the insulation will run]. I am assuming that these baffles are easy to find.
 
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Old 10-03-06, 02:21 PM
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Wink

if its cost some time back they made the rafter baffles out of cardboard you could get some old boxes and make your own. The big box stores have them. Dont forget you need for vents 1 sq ft for every 150 sq ft of attic 1/2 in and 1/2 out.
for a vent fan, attic sq ft X 0.7== the CFM of the fan you need .

ED
 
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